Unsaturated spiro orthocarbonates (SOC) synthesized in these laboratories exhibit polymerization expansion. These crystalline monomer can be made to free radical polymerize. Fine crystals of dimethylene spiro orthocarbonate can be mixed with thinned BIS-GMA based resins to form a comonomer mixture. Polymerization of the SOC lags that of the BIS-GMA unless temperatures above 50 degrees centrigrade are employed. Current research is exploring methods to increase the rate of polymerization of the SOC in order to optimize the expansion (4.5 percent R.T.) of these monomers. Cationic catalyst systems (SnF4 or SnCl4) used in parallel with amine: peroxide systems are being employed. Eutectic mixtures of various SOC monomers will be utilized to reduce the melting temperature of the crystal to increase R.T. polymerization rates. Physical testing involves tensile and compressive strength and tooth adhesion studies employing thermal cycling are conducted on these dental copolymers.